Process for cleaning the seats of double seat valves

ABSTRACT

A process for cleaning the seats of a double seat valve having two independently movable closing elements, each of the closing elements being associated with a respective one of the valve seats, which closing elements can be moved into simultaneous fully open positions when the double seat valve is in an open state, and at least one of the closing elements is movable to a partly open position independently of the other closing element, in which partly open position a passage is defined between said at least one closing element and the seat associated with said at least one closing element, comprising: periodically alternately moving said at least one closing element to the partly open position and reversing the moving to move said at least one closing element to the closed position in partial stroke movements, the reversing of partial stroke movements of the closing elements from opening to closing movement and from closing to opening movement is done by a control unit in response to the passage of time, to the closing elements attaining predetermined positions, or as a function of the flow of cleaning agent.

BACKGROUND OF THE INVENTION

The invention relates to a process for cleaning the seats of double seatvalves and to a control device for applying the process.

A number of control devices of the class characterized above are known[DE 80 03 805 U1, DE 31 08 973 C2, and DE 31 33 273 (2)], all of whichembody the same principle of operation. According to this principle, thedriving piston of the closing element adjusting rod of the closingelement to be lifted within the individual adjustment device is causedto strike a lift limit stop. In this situation the drive piston stopposition can be varied within limits by movable stops inside theindividual movement device (DE 80 03 805 U1), or again the stop positionmay be varied relative to the closing element adjusting rod (DE 31 00973 C2). In the state-of-the-art control device known from DE 80 03 805U1, the individual adjustment devices are integrated into the primaryadjustment device in such a way that one is positioned at the upper andthe other at the lower end of the primary adjustment device.

In the control device known from DE 31 08 973 C2, the two closingelement adjustment rods are guided upward by the primary adjustmentdevice and end in a control cylinder common to both individualadjustment devices. Lastly, DE 31 33 273 C2 describes a control devicein which the individual adjustment devices for both closing elements areintroduced additively below the primary adjustment device generating thefull stroke for the full open position as an independent adjustmentdevice without modification to the adjacent standard components, betweenprimary adjustment device and spacer housing.

The complexity of the state-of-the-art double seat valves for which seatcleaning may be effected is suggestive of the difficulties that may beencountered in presetting of the stop positions for the drive pistons ofthe individual adjustment devices. One difficulty is the sum of themanufacturing tolerances of a great number of relevant componentsnecessitating in each instance individual adjustment of the individualstrokes, to be added to which is the fact that a check must always bemade to determine if the basic operation of the double seat valve isstill ensured within the potential partial stroke adjustment range.Specifically, it is necessary in all cases to prevent displacement ofthe other closing element to a partly open position when one of theclosing elements is lifted for the purpose of cleaning the seat of theelement. Secondly, the valve seat cleaning processes that can be carriedout with state-of-the-art control devices exhibit a fundamentaldisadvantage resulting from stationary retention of a partly openposition of a particular closing element, once this position has beenreached, until the valve seat cleaning process has been ended by acontrol signal fed externally to the double seat valve. Since the drivepiston of the individual adjustment device is caused to strike a stopposition, as has already been pointed out, a more or less large passagecross section is available for the cleaning agent over the entireduration of the particular seat cleaning process. The pressure andtemperature conditions to which double seat valves of the classindicated in the foregoing are subjected in practical applications mayeither reduce or enlarge the passage cross sections that have beenproduced. A reduction may cause inadequate seat cleaning, while in allcases enlargement results in higher cleaning agent consumption, withoutthe cleaning effect necessarily being increased as a result. Especiallyin the event of a large number of double seat valves to be cleanedsimultaneously, as for example within a valve block, this latter aspectnecessitates generation of a too high and thus cost ineffective cleaningoutput, without achievement at least of intensification of the seatcleaning process or seat cleaning of equal intensity for all double seatvalves.

In connection with a state-of-the-art process for realization of aleakage free connecting double seat valve for which seat cleaning ispossible (EP 0 208 126 B1), in which a closing element designed as aslide displaced in the direction of a valve housing element, such as oneguiding a product, for the purpose of cleaning the valve seat, the otherclosing element, designed as a seat plate, being displacedsimultaneously relative to the element, such as one acted upon by aproduct, by the amount of a partial stroke in the same or oppositedirection, it has admittedly been proposed that the seat cleaningprocess be effected by repeated partial stroke movements of the closingelements. The purpose of this measure was primarily to free the seatsurface of the closing element designed as a slide and in the process toapply a film of cleaning agent between the seal seat and seat surface aswell, by means of repeated wiping. The critical area between seat sealand seat surface of the closing element, such as one acted upon by aproduct, could not be cleaned reliably exclusively by a single openingstroke. But even in this state-of-the-art process, the drive pistons ofthe individual adjustment devices are caused to strike against a fixedstop position, which is retained until a control signal supplied fromoutside the double seat valve ends the lifted position over the durationof which the entire passage cross section is available for cleaningagent flow.

SUMMARY OF THE INVENTION

The object of this invention is to increase the cost effectiveness in aprocess for cleaning the seats of double seat valves of the classdescribed in the foregoing, to improve the cleaning effect, and also tosimplify the devices employed for generation of a partial stroke.

The advantages of the proposed process and of the control deviceemployed for application of the process are obvious. Since the change ofdirection of the closing element, the reversal of its opening andclosing movement, occurs periodically, the flow of cleaning agentincreases over the passage cross section, continually varying from aminimum to a maximum amount between closing element and associated valveseat, thus triggering a particularly intensive cleaning action. Themechanical action of the flow is heightened with increase in the rate offlow in the narrowing gap, while separation phenomena and eddy currentsoccur with greater intensity with enlargement of the passage crosssection, this promoting separation and removal of separated foulingsubstances.

The process is further characterized by three process alternatives asregards reversal of movement from opening to closing. One option is tomake reversal dependent exclusively on time, in which case anadvantageous implementation of the process provides for generation ofthe control signals either by a main control unit mounted outside thedouble seat valve or by a control unit mounted on the double seat valveand associated exclusively with it. The stroke-dependent solutionconsists either of introducing reversal of the closing element when aspecific stroke position has been reached or of deriving the controlsignals for reversal directly from the behavior of a detectable physicalquantity corresponding to the stroke-time behavior. An example of such aquantity is the pressure of the pressure means for these individualadjustment devices used to generate the partly open position; thispressure impinges on a pressure sensor or pressure switch and triggersthe control signals by way of these elements. The third alternativesolution involves making the reversal of direction of the closingelement dependent on the flow of cleaning agent; specifically, theclosing movement is introduced if cleaning agent flows through anaperture gap, while the opening movement is initiated if cleaning agentflow is absent. The control signals required for the sequencing of theperiodically alternating opening and closing movements of the closingelement and for reversal of direction are, as it were, generated by theproposed control device in both of the last-named alternative solutions(reversal controlled by stroke and result or by cleaning agent), andnot, for example, by control signals introduced from the environmentexternal to the double seat valve. Such is the case, for example, intime-dependent reversal when the control signals required are emitted bya main control units mounted outside the double seat valve. Anotheressential advantage of the measures proposed is represented by the factthat the entire control process may be effected without mechanicalstroke limit stops, so that no movable stops requiring adjustment arenow needed to ensure the stop position of a particular drive piston ofan individual adjustment device. The new process may still be applied toadvantage, however, if the control device for application of theprocess, as is provided by an advantageous embodiment, is provided witha mechanical stroke limit stop. As one alternative, this mechanicalstroke limit stop may be represented by a safety stop for the particularclosing element, one preventing the double seat valve from reaching itsfully open position in the course of seat cleaning in the event offailure or defective operation of the control device. As another option,the stroke limit stop may be used systematically to limit mechanicallythe final stage of the opening movement, regardless of how reversal ofthe opening to closing movement, and vice versa, are accomplished.

In addition to the intensification of the seat cleaning processdependent on flow mechanics as described in the foregoing, improvementin cleaning of the critical areas between seat seal and closing elementis achieved as a result of the fact that, because of the periodicopening and closing movements of the closing element as the cleaningagent acts, the seal is repeatedly deformed and worked, this resultingin micromovements of the seal relative to the closing element surfaceslimiting the seal.

It is moreover in the nature of things that over the entire seatcleaning period a smaller amount of cleaning agent travels between anpassage cross section periodically alternating between a minimum and amaximum value and an associated valve seat than a stroke partly openstationarily during the entire period over the maximum passage crosssection. This advantage of the process proposed becomes particularlyapparent when the seat areas of a large number of double seat valves areto be cleaned roughly at the same time, because it may then be assumedthat the maximum throughputs for the individual valve are statisticallydistributed over time with the passage cross section fully open for abrief period, so that it is highly probable that a case will never arisein which all double seat valves to be cleaned roughly at the same timewill require the maximum possible flow of cleaning agent. The pressureloss in the line connecting the sequentially engaged valves is thuslimited, that is to say, the first and the last valves in the seriesundergo cleaning of more or less equal intensity.

An advantageous application of the process provides that the stroke-timebehavior of the opening and closing movement of the closing element maybe optionally and independently adjusted. By means of this measure,firstly, influence is exerted on the fluidic processes inside theaperture gap, and secondly, the passage cross section effectively activefor the cleaning agent can thereby be controlled over the cleaningperiod.

The process proposed may be applied to all the control devices indicatedin the foregoing, insofar as the arrangement of the individualadjustment devices, the varied embodiments of the closing elementadjustment rods, and lastly the closing element embodiments areinvolved; the latter may be designed, for example, both as seat platesor both as closing elements designed as slides, or the one may bedesigned as a seat plate and the other as a slide. The closing elementconfigurations may be designed with or without pressure equalizationpistons.

In keeping with the three alternative processes proposed, controldevices are proposed that are independent of each other. Achievement ofthe time-dependent reversal of the opening to closing movement and viceversa requires control signals that are generated by way of a timefunction element. This time function element may be contained in a maincontrol element situated outside the double seat valve. However, it mayalso be mounted locally, that is, in or on the double seat valve, and isactivated there only if the pertinent double seat valve is activated forseat cleaning. The closing element involved periodically executesopening and closing movements in response to the control signalsemitted; the points of reversal of the closing and the opening movementmay be positioned a specific distance from the surface of the seat or astroke limiting stop that may be present. Situations are also possible,however, in which reversal points are situated precisely at the closingor stop position of the closing element or are mandatorily determined bythis position.

The closing element adjustment rods are all provided with a positionindicator for the purpose of production of the proposed control deviceaccomplishing stroke-dependent reversal. This indicator may, forexample, be in the form of cams or recesses acting mechanically on aslave positioner associated with the pertinent closing elementadjustment rod. However, they may also be electric induction masterpositioners. Also suitable as slave positioners, on the other hand, are,for example, electric, compressed-air, or hydraulic switches which, asindicated in the foregoing, may be acted upon by mechanical or electricmeans. Provision is additionally made in the control device for controlby the positioning element either of means for manipulation of driveenergy for the individual adjustment device associated closing elementadjustment device or for direct operation. Such means are customarilyelectrically, pneumatically, or hydraulically controlled positioningvalves by means of which the pressure means, preferably compressed air,is delivered to the individual adjustment device or is forwarded fromit.

It is obvious that the examples of embodiment of a control device forapplication of the process proposed presented in the context of thisinvention are exclusively of the nature of examples. The process may, ofcourse, also be applied to other individual adjustment devicesultimately serving the purpose of generating an adjusting movement ofany nature of the closing element (preferably translatory or rotatory)by way of its closing element adjustment rod. Purely electromotive oragain hydraulic drives may be involved; the closing movement need not,as is customary, necessarily be of the nature of closing by springaction but may also be accomplished by the movement in the seconddirection of a drive acting two directions.

Nor is the process indicated restricted exclusively to the previouslypresented configurations of main adjustment device and individualadjustment devices such as reflect the state of the art. The process mayrather also be applied to drives not previously applied in the case ofdouble seat valves of the class described in the foregoing, ones suchare described in previously referenced EP 0 208 126 B 1, for example.

BRIEF DESCRIPTION OF THE DRAWINGS

The process proposed and the control device for application of theprocess are described with reference to a preferred embodiment asillustrated in the figures of the drawing and described in greaterdetail below.

FIG. 1 presents a diagrammatic representation of a control device asapplied to a double seat valve with two closing elements in the form ofseat plates and in conjunction with possible layouts of main adjustmentdevice and individual adjustment devices, and

FIG. 2 shows a stroke-time pattern h=f(t) of a closing element such asoccurs in use of the control device shown in FIG. 1.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows four areas I to IV characterizing the double seat valvewith the control device for application of the process proposed. Area Iincludes the double seat valve 1 in the area of its valve housing 1a, inan embodiment frequently employed, in which the closing elements 2 and 3are designed as seat plates. In the position shown, the latter formbetween themselves and the valve housings 1a, 1b a leakage cavity 4 thatis connected to the vicinity of the double seat valve by way of a pipe2a connected to the subjacent closing element 2. Both closing elements 2and 3 are actuated by a closing element adjusting rod 5 or 6, both ofwhich extend upward from the valve housing 1a, the latter being designedas a hollow rod and concentrically enclosing the former.

The area II exhibits possible configurations of a main adjustment device12 in communication with individual adjustment devices 11. As viewedfrom left to right, it is a question of a drive configuration such as isset forth in DE-PS 31 08 973, DE- PS 31 33 273, DE-GM 80 03 805, and EP02 208 126. 11a and 11b designate a pressure means connection of theindividual adjustment device 11, and 12a designates a pressure meansconnection of the main adjustment device. The closing element adjustingrods 5 and 6 are in all instances introduced into the driveconfiguration. The individual adjustment devices 11 are provided withand emptied of pressure means by way of pressure means lines 10, 10*.

The areas III and IV contain the control device proper for applicationof the process proposed, only detection of the stroke of the closingelement adjusting rod 6 designed as a hollow rod being shown. A groovedrecess 6a acts as master positioning element, while a position detector7* is designed as a two-point electric switch mounted so as to bemovable in the direction of the stroke. In the double seat valve asactually produced, the area IV is to be found where the closing elementadjusting rod 6 designed as a hollow rod is accessible for the purposeof rod stroke detection.

In the area III, the stroke of the closing element adjusting rod 5 isdetected by another positioning element 5a and a position indicated, asdescribed above for the area IV. The first and the second positiondetectors 7 and 7* are acted upon by a control agent U or U* which isgenerally available as direct or alternating voltage. Means 8, 8a or 8*,8a* are activated as desired by means of the control agent indicated foroperation of the drive energy for the individual adjustment device 11associated with the closing element adjusting rod 5 or 6. It isgenerally a question with the means indicated of electrically actuatedpositioning valves for pressure means, compressed air in particular, theelectric drives being designated as 8a and 8a* and the positioningvalves as 8 and 8*. The pressure means supply is designated as P; thepressure means itself is delivered to the positioning valve 8 or 8* byway of an adjustable choke 9 or 9* and discharged from the valve intothe environment A or A* by way of a similar choke 9a or 9a*. Thepositioning valves 8 or 8* switch the pressure agent line 10 or 10* tothe individual adjustment devices 11.

A signal generator 7** responding to the flow of cleaning agent anddelivering control signals suitable for activating the drive 8a or 8a*of the positioning valve 8 or 8* is to be seen in area I in a position,as viewed in the direction of flow, beyond the valve seat to be cleaned.In the sample embodiment, it is in the leakage cavity 4.

The mode of operation of the control device is to be explained inconjunction with the stroke-time behavior h=f(t) as illustrated in FIG.2. The position detector 7, for example, is positioned in the directionof the stroke so that a larger partial stroke designated as H in FIG. 2is set. The pattern of the opening stroke over time is designated as a,and that of the closing stroke b. The total time of a switching intervalis designated as Δt_(ges). It must be noted here that no mechanicalstroke limiting stop whatever is employed in this instance to secure thegreatest partial stroke H. If the closing element adjusting rod 5 is nowmoved upward far enough so that the positioning element 5a in the formof an annular groove actuates the position detector 7, operation of thedrive 8a of the positioning valve 8 is interrupted as a result. Thelatter opens the pressure means line 10 leading to the environment A,and the pressure means can escape from the individual adjustment device11. The closing element adjusting rod 5 and the closing element 2connected to it now move downward. As soon as the positioning element 7aleaves the area of influence of the position detector 5a in the processof movement downward, the latter again activates the drive 8a, and thepressure means can flow again from the pressure means supply by way ofthe positioning valve 8 of the individual adjustment device 11 along thepath through the pressure means line 10. The closing movement comes to ahalt, the closing element 2 is on or in the vicinity of its seatingsurface, a reversal of direction takes place, followed by a repeatedopening movement of the closing element 2. Both the supply and removalof pressure means into and from the individual adjustment device 11 canbe acted upon by means of the adjustable choke 9 or 9a. It is possiblethereby to act upon an increase in the opening stroke a or the closingstroke b in the stroke pattern over time. The increase may also beaffected by additional storage devices, not shown or designated, thatincrease the volume of the individual adjustment devices 11. Whether ornot the closing element 2 comes to rest at the end of its closing strokeon the metal, on the associated seating surface, depends essentially onthe parameters selected that determine the periodic pattern ofalternating opening and closing movements over time. In the caseillustrated, in FIG. 2, brief metal contact occurs between closingelement 2 and the associated valve seat, since the closing stroke breaches the line identified by zero. H* in FIG. 2 designates theclearance stroke of the closing element 2 to the point of lifting of theseat seal away from the associated valve seat. This means that a passagecross section for the cleaning agent is available only from this pointforward as the opening stroke continues. In the case in question theinterval for the effective opening stroke amounts to S =H-H* As is alsoto be seen from FIG. 2, passage of cleaning agent to the area of theseat remains blocked over interval Δt₁, while cleaning of the seat withconstantly varying passage cross section, increasing from zero to amaximum and then decreasing again to zero takes place over the intervalΔt₂. The advantages obtainable with a seat cleaning process of this kindhave already been discussed at length in the foregoing.

The pattern illustrated in FIG. 2 also makes it abundantly clear thatadditional opening intervals of other double seat valves alsosimultaneously subordinated to the proposed seat cleaning process mayfrom the statistical viewpoint be placed in the area between theeffective opening intervals, without the need for linear increase in thecleaning output to be made available with increase in the number ofvalves waiting for seat cleaning. If the positioning valves 8 or 8* areactivated as a function of the flow of cleaning agent by a signalgenerator 7** responding to the flow of cleaning agent at a point beyondthe valve seat to be cleaned, as viewed in the direction of flow,detection of the pertinent closing element stroke along the path overthe position detectors 5a or 6a in conjunction with the positiondetector 7 or 7* is superfluous. As soon as a flow of cleaning agent isestablished as a result of effective opening of the passage gap betweenclosing element 2 or 3 and the associated valve seat, a resulting signalfrom the signal generator 7** causes reversal of the opening to closingmovement. Interruption of the flow of cleaning agent as the closingmovement continues now results in a signal reversing the process, sothat the sequence of periodically alternating opening and closingmovements is ensured.

In order on the one hand of prevent transfer to the double seat valve toits fully open position during seat cleaning in the event of failure ordefective operation of the control device, each individual adjustmentdevice 11 is provided with a mechanical stop, not shown in the drawingthat makes it possible to limit the individual stroke of the pertinentindividual adjustment device 11 to an amount greater than that of theeffective opening stroke H in the pertinent seat cleaning process. Onthe other hand, this stop is also suitable for producing the systematiceffective opening stroke within the framework of the process proposed bycausing the individual adjustment device to come into contact with thisstop.

I claim:
 1. A process for cleaning the seats of a double seat valvehaving two independently movable closing elements, each of the closingelements being associated with a respective one of the valve seats,which closing elements can be moved into simultaneous fully openpositions when the double seat valve is in an open state, and at leastone of the closing elements is movable to a partly open positionindependently of the other closing element, in which partly openposition a passage is defined between said at least one closing elementand the seat associated with said at least one closing element, saidprocess involving flow of a cleaning agent, said processcomprising:periodically alternately moving said at least one closingelement to the partly open position and reversing the moving to movesaid at least one closing element to the closed position in partialstroke movements, the reversing of partial stroke movements of theclosing elements from opening to closing movement and from closing toopening movement is done by a control unit in response to a passage oftime.
 2. A process as claimed in claim 1, wherein a stroke-time patternof the opening movement and a stroke-time pattern of the closingmovement are set as desired and independently of each other.
 3. Theprocess according to claim 1, wherein the partial stroke movements ofsaid at least one closing element are reversed by a main control unitoutside the double seat valve.
 4. The process of claim 1, wherein thepartial stroke movements of said at least one closing element arereversed by a control unit associated exclusively with the double seatvalve.
 5. A process for cleaning the seats of a double seat valve havingtwo independently movable closing elements, each of the closing elementsbeing associated with a respective one of the valve seats, which closingelements are movable into simultaneous fully open positions when thedouble seat valve is in an open state, and at least one of the closingelements is movable into a partly open position independently of theother closing element, in which partly open position a passage isdefined between said at least one closing element and the seatassociated with said at least one closing element, said processinvolving flow of a cleaning agent, said process comprising:periodicallyalternately moving said at least one closing element to the partly openposition and reversing the moving to move said at least one closingelement to the closed position in partial stroke movements, thereversing of partial stroke movements of said at least one closingelement from opening to closing movement and from closing to openingmovement is done in response to the closing elements attaining specificpositions.
 6. The process of claim 5, wherein the attaining of thespecific positions by said at least one closing element is detected bydirectly sensing the positions of said at least one closing element. 7.The process of claim 5, wherein the attaining of the specific positionsby said at least one closing element is detected indirectly by sensing aphysical quantity associated with the positions of said at least oneclosing element.
 8. The process of claim 7, wherein the closing elementsare moved by adjustment devices operated by a pressure medium, and thephysical quantity is the pressure of the pressure medium for theadjustment devices.
 9. A process for cleaning the seats of a double seatvalve having two independently movable closing elements, each of theclosing elements being associated with a respective one of the valveseats, which closing elements are movable into simultaneous fully openpositions when the double seat valve is in an open state, and at leastone of the closing elements is movable into a partly open positionindependently of the other closing element, in which partly openposition a passage is defined between said at least one closing elementand the seat associated with said at least one closing element, saidprocess involving flow of a cleaning agent, said processcomprising:periodically alternately moving said at least one closingelement to the partly open position and reversing the moving to movesaid at least one closing element to the closed position in partialstroke movements, the reversing of partial stroke movements of said atleast one closing element from opening to closing movement and fromclosing to opening movement is done as a function of the flow ofcleaning agent.
 10. The process of claim 9, wherein the flow of cleaningagent has a direction and the partial stroke movements of said at leastone closing element are reversed as a function of the flow of cleaningagent at a point beyond the valve seat to be cleaned, as viewed in thedirection of flow.